Phantom Shock in a Patient With an Implantable Cardioverter Defibrillator: Case Report

ICDs are now routinely used as prophylaxis and as a rescue treatment for patients prone to malignant ventricular arrhythmias. This case study describes a patient who experienced a phenomenon known as “phantom shock,” a term which implies that the patient perceives an ICD shock, even though the memory of the ICD indicates that no therapy (shock) was delivered. In cases such as these, the author believes it is imperative that nurses support the patients and not minimize their perceptions and review the device’s history.Introduced clinically in 1980 and approved by the Food and Drug Administration for implantation in 1985, implantable cardioverter defibrillators (ICDs) are now routinely used as prophylaxis and as rescue treatment for patients prone to malignant ventricular arrhythmias.1 The current devices are capable of monitoring and pacing in both the atria and the ventricles and of delivering antitachycardia pacing and low-energy or high-energy shocks to treat tachycardias. Whereas older versions of the ICD required an open-chest procedure for implantation and leads with epicardial pads, most newer systems are implanted by using transvenous leads, with the device tucked under the skin of the upper part of the chest. Implantation of these devices has resulted in a more effective and efficient method of treating potentially lethal arrhythmias in a wide variety of patients, such as those with primary electrical disturbance, certain cardiomyopathies, arrhythmogenic right ventricular dysplasia, long QT syndrome, and a history of sudden cardiac death.With estimates of 250 000 to 300 000 ICDs implanted to date worldwide, the benefits of immediate defibrillation for patients’ survival are clearly recognized.1,2 However, acknowledgment is growing among practitioners about the coexistence of various types and degrees of psychological disorders in these patients.3–7 The emotional responses after ICD implantation that have been studied most are anxiety and depression, which are common in patients with coronary artery disease.2,4,6–9 A recently recognized phenomenon that occurs in some patients with ICDs and may be a manifestation of an emotional response is called a “phantom shock.”10,11 The term phantom shock implies that the patient perceives an ICD discharge with describable sensations, even though the memory of the ICD indicates that no therapy (shock) was delivered. The following case report describes a patient who experienced this phenomenon.Mr W. is a 60-year-old man who had a Medtronic 7223 ICD (Medtronic, Minneapolis, Minn) implanted after a coronary artery bypass graft procedure for severe coronary disease, as part of a study protocol in 1998. His medical history includes a 30-pack-year smoking history, idiopathic dilated cardiomyopathy, a left ventricular ejection fraction of 0.26, coronary artery disease, hypertension, cerebellar cerebral vascular accident, insulin-dependent diabetes mellitus, and chronic renal insufficiency. In April 1999, Mr W. received his first 5 shocks for ventricular tachycardia and an episode of ventricular fibrillation. The first 4 shocks were unsuccessful in converting his rhythm, so his device was reprogrammed. After a noninvasive programmed stimulation study, the amount of energy the device delivers with each shock was increased from 21 to 31 J to ensure consistent rhythm conversion. Two months later, Mr W. came to the emergency department because he thought he had received a shock from his ICD. When the device was interrogated, no evidence was found that a shock had been delivered. The following week, Mr W. returned to the emergency department because of 2 more ICD firings. He described the shocks as “raising me off the bed.” Again, no events had been recorded in the device’s memory.Several days later, he came to the clinic with a notation on his calendar that the device had fired several times. Interrogation of the ICD revealed no detections of tachycardia and indicated that no therapy had been delivered since his last visit. Mr W. was adamant that the device had fired on each occasion, asserting that these discharges felt similar to the discharges he experienced in April. He said that he had not had any prodrome or signs or symptoms before these perceived shocks. A thorough testing of the ICD, including evaluation of its sensing and pacing threshold, indicated that it was functioning appropriately. Because Mr W. was convinced that the device had fired, Medtronic technical services were consulted to determine whether a device might spontaneously discharge without documentation of an event in the counters. This possibility was deemed highly unlikely. However, in an attempt to determine if Mr W. was experiencing an event that was not being recorded by the device, a looping event recorder was applied, and he was instructed to trigger the recorder when he perceived a shock.Within 3 days, Mr W. had transmitted 3 captured “events” when he triggered the event recorder because of perceived shocks. These 3 events revealed sinus rhythm. In the next 5 months, he was examined in the clinic and emergency department because of 5 more perceived shocks. Interestingly, during this time, he had a true discharge for ventricular tachycardia and fibrillation, which he did not report but was found incidentally during a routine follow-up visit. Mr W. began to appear disheveled and tired, and he reported that he was not sleeping well.During a visit to the emergency department for a perceived shock, Mr W. and his family, who were all quite concerned that the device was actually shocking him but was not recording anything, expressed concern over the validity of the examinations of the ICD and the looping event recorder. Accordingly, approximately 8 months after he had received 6 documented shocks and had reported and been evaluated for some 15 other events, Mr W. had an insertable looping event recorder, the Medtronic Reveal, implanted. This thin, thumb-sized device was programmed to automatically record heart rates that occurred outside preset parameters and to record events when triggered by the patient.Within 8 days of receiving the implant, Mr W. reported to the clinic, stating that his ICD had “gone off ” and he had triggered the Reveal. One week later, he reported that the device had fired 3 additional times during a 2-day period. Interrogation of both the ICD and the Reveal each time indicated no arrhythmias. All recorded events on the Reveal were sinus rhythm. In the next 2 months, Mr W. reported 3 more “shocks,” and during a visit to the emergency department in which he was told that he had not received a shock, he became agitated and signed himself out against medical advice. At each of 2 subsequent quarterly visits to his cardiologist, Mr W. reported interim ICD firings (2–3 shocks), but again no documentation was found within the ICD counters, no electrograms had been stored, and triggered Reveal episodes showed only sinus rhythm.No evidence was found to support Mr W.’s reports of multiple ICD firings, despite efforts to obtain independent verification with event recorders. The nurses caring for Mr W. were concerned about his psychological state. A married man who had worked all of his life as a baker, until forced to retire in 1996 because of health problems, Mr W. had recently begun to have signs and symptoms that are often indicative of depression: poor sleeping, lack of attention to appearance, and increasing agitation. Mr W. and the staff were frustrated because no clear explanation for his experiences had been found.A subsequent search of the literature revealed only 2 references to a phenomenon in which ICD patients experienced the perception of a shock when, in fact, none was delivered.10,11 It was thought that Mr W. might be experiencing such a phenomenon. This possible explanation was discussed with Mr W. in very basic terms, with the caution that little research has been done on this phenomenon. Because of the growing concerns that Mr W. might be experiencing depression, he was given a prescription for an antidepressant. However, it was later determined that he did not have that prescription filled.By January 2001, Mr W. continued to report that he was receiving shocks (~25–30 total phantom shocks since the ICD was implanted), but he was no longer coming into the clinic or emergency department for immediate interrogation of the device. He appeared calmer about these perceived shocks, exuding an air of sad resignation. As of September 2001, he was having only rare phantom shocks and experienced no real discharges of the ICD. He was better kempt in appearance, although he had been hospitalized several times in previous months for renal complications. He reported, “I am doing OK; I guess sometimes my mind plays tricks on me with this box.”Mr W.’s case illustrates the vagaries of patients’ responses to illness and treatment. Members of our team had seen only rare, isolated incidents of perceived but not documented shocks. In this instance, the sheer number of perceived shocks and Mr W.’s adamant certainty that they had truly occurred, coupled with our lack of another reasonable explanation for them, provided sufficient impetus for us to take the additional step of implanting an event recorder. Mr W.’s experience may be a more dramatic manifestation of a real, yet underdescribed phenomenon.Recognizing this phenomenon of perceived shocks, Swygman et al10 reported that 30 of 445 patients with ICDs studied reported phantom shocks. The authors investigated frequency of occurrence and possible predictors (age, sex, ejection fraction, total number of shocks, appropriate vs inappropriate shocks). No predictors were found, but Swygman et al noted that these phantom shocks occurred more commonly in the first 6 months after an ICD was implanted but occurred as late as 52 months after the ICD was implanted in 1 patient.I have cared for 11 patients who have experienced this phenomenon. Three of these patients experienced numerous true discharges as well as phantom shocks. Interestingly, these patients described the perceived shock in terms similar to those they used to describe actual shocks, and the episodes of perceived shocks often occurred early in the morning or when the patients were at rest. These accounts echo the observance of “nocturnal phantom shocks” described in a letter to the New England Journal of Medicine in which Kowey et al11 posited that such experiences, noted in 84 patients in their practice, indicated maladjustment to the ICD.Although clearly a relatively rare occurrence, the phenomenon of phantom shocks can have widespread effects on patients’ use of healthcare resources, adjustment to the ICD, and quality of life. This case study emphasizes the need for further study of the psychological mechanism behind phantom shocks and the need for determination of possible treatment options. To that end, I have initiated a study to determine the prevalence and extent of anxiety or depression in patients who experience phantom shocks. Additionally, nurses and other healthcare professionals should be cognizant of this phenomenon and its potential effects on patients, while maintaining the belief that all “discharges” should be reviewed. As in this case, a patient can have both documented and phantom shocks. It is imperative that nurses support the patient, review the device’s history, and avoid the impulse to minimize the patient’s perceptions. Acknowledging a patient’s perception of a phantom shock as a real experience promotes continuing communication and fosters a trusting relationship.